In most conventional integrated circuit (IC) manufacturing processes, a semiconductor wafer to be processed is placed inside a process chamber and atop a chuck, where it is typically held in place. Such chucks typically have a diameter that is slightly less than that of the semiconductor wafer, such that the wafer can overhang the chuck by a small amount around the entire circumference of the chuck surface. Prior to processing, the semiconductor wafer is usually positioned on the chuck such that the center of the wafer lies on or near the center of the chuck, with both the wafer and the chuck residing in substantially parallel horizontal planes. One surface of the wafer, which is designated as the bottom or inactive side, is the one that is placed in contact with the chuck, while the opposite top surface is designated as the active surface to be processed.
Processing of the wafer can be accomplished via a variety of techniques and methods well known in the art, such as various CVD, PVD, spray and spin coating procedures. During a typical spin coating procedure, for example, which is usually performed through use of a rotating chuck, one or more coating materials are applied to the semiconductor wafer by flowing at least one liquid coating material onto the top surface of the wafer while it is spinning. As the chuck rotates, a liquid coating material, such as a photoresist, is then applied at the wafer center. The centrifugal force of the rotating wafer then causes the liquid coating material to spread radially outward from the center of the wafer towards the edge, such that the top of the wafer is substantially evenly coated with the liquid coating material.
Photoresist, polyamide, and other spin-coated materials are typically spun onto the semiconductor wafer in a sticky form, which when dried becomes brittle, such that the material has a tendency to crack, chip, flake or even shatter where the spun on film is too thick. Although such effects can result in defects in the finished wafer, film thickness for the majority of the wafer is usually controlled throughout the spin on operation and in a subsequent drying or heat treatment step. This is not usually the case, however, for any spun on liquid that travels to the edge of the wafer or to the wafer backside. While it is desirable that excess coating material be ideally ejected or sucked away from the edge of the wafer, more often than not some coating material will invariably collect at and form a bead along the edge of the wafer.
On occasion, excess coating material may even curl around and under the wafer to collect and rest along the backside of the wafer. These “edge beads” and “backside deposits,” as they are called, tend to be irregular by nature, and if not accounted for will almost invariably result in the kind of cracking, chipping and flaking that accompanies a coating film that is too thick or otherwise irregular. Furthermore, any coating material that has crept around to the backside of the wafer during the spin coating process can not only become a source of particulate contamination, but can also prevent proper leveling and focusing of a lithography tool during any potential subsequent photoexposure step.
Accordingly, a common follow up step after any spin coat step or steps in the wafer manufacturing process is to dispense a solvent, such as ethoxypropanol (EEP) at or near the edge of the wafer to dissolve the edge bead and remove any photoresist or other undesirable coating from the edge and/or backside of the wafer. Although some wafer processing systems, such as those employing a frustraconical or similar catch cup design, do not require backside wafer cleaning, virtually all systems and techniques do require at least an edge bead removal or similar process step. In such an “edge bead removal,” “backside wash,” and/or “wet edge bead operation” cleaning step, a solvent is typically sprayed via nozzle to the bottom and/or top surfaces of the wafer near the outer edge while the wafer is spinning. This solvent, which is sometimes referred to as edge bead removal (EBR) fluid or solvent, can be sprayed onto the backside edge of the wafer, in which case it usually spreads outward and curls up and around to the top of the wafer to dissolve the edge bead during a spray and spin process. Alternatively, this solvent can be dispensed directly onto the top edge of the wafer, whereby it usually spreads outward and curls around toward the bottom of the wafer to dissolve the edge bead.
Various apparatuses and methods for depositing a spin coated film on a semiconductor wafer and cleaning up edge beads and backside deposits are well known, and instances of such apparatuses and methods can be found, for example, in U.S. Pat. Nos. 6,062,288; 6,033,988; 5,952,050; 5,952,045; 5,939,139; 5,911,090; 5,868,843; 5,718,763; 5,688,411; 5,444,921; 5,294,257; 4,732,785; 4,668,334; and 4,113,492, for example, all of which are incorporated herein by reference in their entirety. As mentioned in some of these references and elsewhere, one or some combination of one or more top and bottom nozzles as outlined above is frequently employed for purposes of edge bead removal and backside wash. In most such cases, however, such processes allow solvent and dissolved photoresist to be splashed about, which often leaves an undesirably jagged edge profile on the photoresist or other coating material, which in turn tends to result in wafer defects at those locations.
In addition, the use of only one nozzle is often insufficient to provide enough solvent over enough of an area to result in an adequately complete backside wash and edge bead removal for an entire wafer. Furthermore, most semiconductor wafers are not perfectly round, as many have one or more flattened areas or “flats” along the outer circumference in order to better facilitate other steps of the wafer manufacturing process. Such a flat on a wafer is a region that is particularly susceptible to irregularities in spin coated films, and many edge bead removal and backside wash techniques do little or nothing to account for the irregular nature of the “flat” region of a wafer. As a result, edge beads tend to be more prevalent in such regions, with the accompanying rise in wafer defects as well.
Accordingly, there exists a need for improved apparatuses and methods for cleaning semiconductor wafers during and after the processing of same, and more particularly, for such apparatuses and methods to provide better and more reliable results in an edge bead removal and backside wash process, especially at or near the flat regions of such wafers.